Priority is being claimed from Japan Application Nos. 154,761/91 and 154,762/91, both of which were filed on Jun. 26, 1991.
1. Field of the Invention
This invention relates to a process for manufacturing an abrasive tape that is suitable for finish lapping of precision electronic parts or precision machinery parts, for example, magnetic discs, magnetic heads, etc., precision surface finish abrasion of molds and other similar works.
2. Discussion of the Art
The surfaces of most precision electronic parts and precision machine parts are required to be finished to a high degree of accuracy with unevenness of micron or submicron order. For meeting this requirement, there are used lapping films or tapes having an abrasive layer formed on a substrate made of a film, synthetic paper, or the like by coating the substrate with a resin solution having dispersed therein inorganic particles of high hardness and drying the coating.
The abrasive layer in conventional abrasive tapes is generally formed by applying on a substrate a coating solution prepared by dispersing inorganic abrasive particles in a solution of a thermoplastic, thermosetting, or reactive resin as a binder, and conducting the appropriate aftertreatment according to the kind of the resin in the coating solution.
In most conventional abrasive tapes, polyester resin having a molecular weight of around 20,000 and crosslinked by a trifunctional isocyanate is used as binder.
Use of such a binder, however, because of low density of OH groups in polyester resin, tends to lower the rate of reaction with isocyanate, necessitating a long reaction time and a high reaction temperature, such as 36 hours at 70.degree. C. and about 80 hours at 50.degree. C. Further, when the film is wound up into a roll and cured at a high temperature, variation in film qualities such as cut performance and finishing characteristics is caused by variation of internal pressure developed by the winding tension and by variations in temperature distribution resulting in variation of product quality.
Also, abrasive tapes produced by said conventional method are low in crosslinking density of binder and vulnerable to change in quality by internal pressure of the roll in storage.
The present invention has made intensive studies of binder compositions capable of decreasing variation of quality during room temperature curing of abrasive tapes in a roll, and, as a result, discovered that it is possible to obtain an abrasive tape capable of greatly lessened variation of quality occurring during curing and suited for abrading of thin-film type magnetic discs by using a polyester resin having specific characteristics in place of the urethane resin described previously. One aspect of the present invention was achieved on the basis of this discovery.
In addition, the present inventor has made intensive studies of binders for abrasive tape and, as a result, discovered a binder which has sufficiently high reactivity to maintain a sufficiently high reaction rate even when the reaction temperature is lowered to room temperature; the binder also provides high crosslinking density. Another aspect of the present invention was achieved on the basis of such discovery.